This invention relates generally to a device for positioning a medical instrument, and more particularly to an adjustable support and positioning device for an ultrasound imaging probe.
There are a number of medical procedures that utilize ultrasound images for diagnostic and/or therapeutic purposes. For example, one widely applied minimally invasive procedure for the treatment of prostate cancer is the percutaneous transperineal implantation of radioactive seeds called brachytherapy. This procedure is performed with the patient in the lithotomy position, using an ultrasound imaging probe placed in the rectum to monitor seed placement. Precise and reproducible orientation and positioning of the ultrasound imaging probe in the rectum is a key element in both the calculations required for determining the number and distribution of radioactive seeds required for treatment and their subsequent placement using pre-loaded needles guided by a perineal template and real time ultrasound imaging.
Another form of treatment that is promising is cryotherapy. This procedure is performed with the patient in the lithotomy position, using an ultrasound imaging probe placed in the rectum to guide an instrument called a cryoprobe and to monitor the freezing of the gland. Typically, in cryotherapy, liquid nitrogen or a similar freezing agent is circulated through the cryoprobe, which is placed in contact with the tumor. The tumor is frozen as is some of the surrounding tissue. Often, the treatments are cyclic in which the tumor is frozen, allowed to thaw, and then refrozen. The goal of this treatment is to rapidly kill the cancer cells without subjecting the surrounding healthy tissue to trauma.
In the field of general surgery, there is a need for detailed visualization of the anatomy of the distal rectum and anus in patients with rectal cancer. High resolution ultrasound imaging of this area has been shown to be of great value in determining whether the cancer extends into the pelvic floor structures. This information is used by the surgeon to decide whether the anal continence mechanism may be saved or whether a colostomy will be required. The use of two dimensional images to construct a three dimensional view for study is considered the state of the art for evaluating these patients.
As these examples illustrate, multiple sequential two dimensional, transverse or radial, high resolution ultrasound images of the human pelvis, distal colon, and rectum are very useful and can be obtained by appropriate use of transrectal ultrasound transducers. In an analogous fashion, multiple sequential two dimensional, high resolution images of other anatomical regions can be obtained using known medical imaging instrumentation. Computer algorithms have been developed that use these images to construct a clinically valuable three dimensional holographic view of the anatomical region of interest. In order to optimize the resolution and accuracy of the generated three dimensional images, accurate sequencing and accurate spacing of the two dimensional image acquisition is essential.
Although manual withdrawal of the imager, such as a transrectal ultrasound transducer, can achieve proper image sequencing, it is a poor method for obtaining accurate image spacing. Presently, there are many homemade and commercially available devices for mounting, positioning and rotating the various commercially available imagers. None of these devices have achieved wide acclaim because of significant limitations in their ease of use and level of precision of probe control and placement.
Mechanized positioners for the imaging tranducers do exist. However, many lack the ability to disengage the motor or other mechanism used to position the imager. Thus, manual positioning of the imager for rapid placement and repeat scans is not possible. Additionally, the risk of accidental patient injury from motor driven insertion exists. Risk of patient injury also exists because of the lack of tactile and other feedback provided by manual movement of the imaging transducers in other mechanized positioners.
Thus, there is a need for an improved medical instrument positioning device.
The present invention relates to a medical instrument positioning device for controlled placement of a wide variety of medical instruments, such as an ultrasound transducer probe. The positioning device comprises a base member having a base and a central shaft operatively associated with the base, a carriage member having a cavity configured and dimensioned to receive at least a portion of a medical instrument and slideably connected to the central shaft, a drive member coupled to the carriage member and engageable with the central shaft for movement with the central shaft and disengageable from the central shaft for sliding movement along the central shaft, and a quick release member operatively associated with the drive member. The quick release member has an inactive configuration in which the drive member engages the central shaft and an active configuration in which the drive member disengages the central shaft.
In one embodiment, the base includes first and second crossbars and first and second elongated, spaced parallel side rails, with the first and second side rails parallel with the central shaft. The central shaft can be threaded and rotatably connected at first and second ends thereof to the first and second crossbars so that rotation of the central shaft with the quick release member in the inactive configuration causes incremental movement of the drive member along the central shaft. In order to provide smooth movement, at least one of the drive member and carriage member can include first and second flanges extending therefrom and the first and second side rails each include a slot for slideably receiving one of the flanges. The drive member can have an engagement member that receives at least a portion of the release lever so that upon actuation of the release member, the engagement member either engages or disengages the central shaft.
In one embodiment, the base is provided with a coupler for connection to a support stand. Furthermore, the carriage member can have a probe securing member to support the medical instrument and a fastener so that the probe securing member and fastener secure the medical instrument in the cavity of the carriage member. The base member can also include at least one scale to provide indicia of displacement of the carriage member along the base member. The scale can cooperate with a carriage scale marker on the carriage member to indicate the numerical position of the carriage member on the base member. In order to couple the device to a motor, the base member can be provided with a rotatable motor engagement member attached at a first end to the central shaft and removably coupled to a motor at a second end. If an electric motor is used, at least a portion of the motor engagement member can be made of a non-conductive material to electrically isolate the motor and the device.
In order to provide some limit on the force used to move the medical instrument, the device can include a safety release element that uncouples the drive member from the carriage member when a movement force on the carriage member exceeds a threshold value. In one embodiment, the safety release element comprises a magnet on the carriage member and a magnet on the drive member. The magnets magnetically couple the drive member and the carriage member. The magnetic field of one of the magnets (either on the carriage member or drive member) can be adjustable to adjust the threshold value. This can be achieved, for example, by making the adjustable magnet movable with respect to the other magnet to thereby adjust the threshold value. A set screw can be used to move the adjustable magnet.
In another embodiment, the medical instrument positioning device comprises a base member having a base and a central shaft operatively associated with the base, a carriage member having a cavity configured and dimensioned to receive at least a portion of a medical instrument and slideably connected to the central shaft, a drive member removably coupled to the carriage member and engageable with the central shaft for movement along the central shaft, and a safety release element that uncouples the drive member from the carriage member when a movement force on the carriage member exceeds a threshold value. In this embodiment, the safety release element can include a first plurality of magnets on the carriage member and a second plurality of magnets on the drive member. The first and second plurality of magnets magnetically couple the drive member and the carriage member. The magnetic fields of at least some of the first and second plurality of magnets can be adjustable to adjust the threshold value.